Method and apparatus for measuring and reporting beams in a beamforming based system

ABSTRACT

The present disclosure relates to a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4th-Generation (4G) communication system such as Long Term Evolution (LTE). Disclosed is a method of reporting beam measurement state information by a User Equipment (UE). The method may include: measuring beam state information by using a first reception chain and a second reception chain; controlling beam state information on the first reception chain to correspond to beam state information on the second reception chain; calculating state information on each beam based on the controlled beam state information on the first reception chain and beam state information on the second reception chain; and reporting state information on one or more beams.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 15/329,439, filed on Jan. 26, 2017, which was a U.S. National Stageapplication under 35 U.S.C. § 371 of an International application filedon Jul. 31, 2015 and assigned application number PCT/KR2015/008046,which claimed the benefit of a Korean patent application filed on Jul.31, 2014 in the Korean Intellectual Property Office and assigned Serialnumber 10-2014-0098580, the entire disclosure of which is herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates generally to beam measurement in acommunication system and an apparatus therefor. Further, the presentinvention relates to a method and an apparatus for measuring a beam in abeamforming system. In an exemplary a cell in a cellular system can becomposed of one or more limited bandwidth beams instead of a typicalsingle omni-directional beam.

BACKGROUND ART

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 GHz bands or 28 GHz bands or 38 Ghzbands, so as to accomplish higher data rates by utilizing the vastbandwidth available in these mmWave bands. To decrease propagation lossof the radio waves and increase the transmission distance, thebeamforming, massive multiple-input multiple-output (MIMO), FullDimensional MIMO (FD-MIMO), array antenna, an analog beam forming, largescale antenna techniques are discussed and proposed to be used in 5Gcommunication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud RadioAccess Networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), and filter bank multi carrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA) as an advancedaccess technology have been developed.

In a general cellular system, measurement samples are acquired during apredetermined period to exclude a shadow effect and a short-term fadingeffect, and then an average is calculated. Thereafter, in order todetermine whether a predetermined event is satisfied, the average iscompared with a preset threshold. For example, it is assumed that ameasurement report is performed when a simple event, such as ameasurement average of a serving cell equal to or smaller than athreshold, is configured. A User Equipment (UE) measures a configuredmeasurement value to perform a proper average calculation process, andthen compares whether the measured average of the serving cell is equalto or smaller than a preset threshold on every measurement period. Whenthe measurement value of the serving cell is equal to or smaller thanthe preset threshold, the UE transmits a measurement report to anevolved NodeB (eNB). Based on the measurement report, the eNB mayperform appropriate tasks such as allowing the UE to measure cells infrequencies different from that of the measurement cell of the currentUE.

FIG. 1 illustrates a process for generally performing a measurementreport procedure according to each layer. Referring to FIG. 1, layer 1(physical layer) performs measurement at for eg. every 40 ms, calculatesan average of values measured in every 200 ms, and reports thecalculated average to layer 3. This is a general measurement resultreport procedure in the LTE system. Layer 3 compares a preset thresholdand the reported average. Layer 3 performs a process of calculating anaverage of different times according to an averaging parameter set tocalculate the final filtered value, which when a final filtered valuemeets the preset threshold triggers reporting of the measured value.

Alternatively, the same average value calculation process may be used.When the periodic measurement value report is configured, measurementvalues may be reported to the eNB.

A general layer 3 average calculation in LTE is performed based on anequation of (1−a)*Fn−1+a*Mn. In the equation, a denotes a filtercoefficient, Mn denotes an nth layer 1 average, and Fn−1 denotes ann−1th layer 3 average.

Various events, which can be configured in the LTE system, are shown inthe below table.

Event 3GPP TS 36.331 A1 Serving > Threshold A2 Serving > Threshold A3Neighbor > Pcell + Offset A4 Neighbor > Threshold A5 Pcell < ThresholdNeighbor > Threshold 2 A6 Neighbor > Scell + Offset

Cells, which meet a reference for reporting (meet preset thresholds) arearranged and reported in a descending order of measurement values later.A reporting configuration may be configured as the maximum number ofcells, to which the report can be provided (for example, a general valueis 8).

Measurement values in LTE may be received signal received power (RSRP)or received signal received quality (RSRQ).

Meanwhile, in a cellular system based on the millimeter wave, it isrequired to overcome a high propagation loss in order to actuallyoperate the cellular communication system, so that beamforming isneeded. For example, in order to operate a cellular system based onmillimeter wave band up to a range of 200 meters, a beam width of about10 degrees is required.

Further, the beamforming requires a method of measuring each beam,reporting a measurement result, and using the measurement result forselection of the best beam(s) for communication with the base station.

DISCLOSURE OF INVENTION Technical Problem

An aspect of the present invention is to provide a method and anapparatus for measuring a cell in a communication system (for example, abeamforming system).

Solution to Problem

In accordance with an aspect of the present invention, a method ofreporting beam measurement state information by a terminal is provided.The method includes: measuring beam state information on beams of atleast one serving cell and beams of at least one neighbor cell;adjusting beam state information on at least one measured beam fornormalizing the beam state information on the measured beam; calculatingstate information on each beam based on the adjusted beam stateinformation; and reporting state information on one or more beams.

In accordance with another aspect of the present invention, a terminalfor reporting beam measurement state information is provided. Theapparatus includes: a transceiver configured to transmit and receive asignal; and at least one processor configured to: measure beam stateinformation on beams of at least one serving cell and beams of at leastone neighbor cell; adjust beam state information on at least onemeasured beam for normalizing the beam state information on the measuredbeam; calculate state information on each beam based on the adjustedbeam state information; and report state information on one or morebeams.

In accordance with another aspect of the present invention, a method ofreceiving beam state information by a base station is provided. Themethod includes: transmitting beam state information reportconfiguration information to a terminal; and receiving beam stateinformation from the terminal based on the beam state information reportconfiguration information, wherein the beam state information isdetermined based on information, which is generated by adjusting beamstate information measured by the terminal for normalizing.

In accordance with another aspect of the present invention, a basestation for receiving state information is provided. The apparatusincludes: a transceiver configured to transmit and receive a signal; andat least one processor configured to; transmit beam state informationreport configuration information to a terminal; and receive beam stateinformation from the terminal based on the beam state information reportconfiguration information, wherein the beam state information isdetermined based on information, which is generated by adjusting thebeam state information measured by the terminal for normalizing.

Advantageous Effects of Invention

According to an embodiment of the present invention, it is possible toprovide a method and an apparatus for efficiently measuring a cell in acommunication system (for example, a beamforming system).

According to various embodiments, it is possible to provide a method ofpreventing a difference between a beam pair in beam selection. Anembodiment of the present invention can provide a method of determininga cell priority based on a beam pair. Further, an embodiment of thepresent invention can provide a method of defining a reporting event fora beamforming system.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptionin conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a process for generally performing a measurementreport procedure according to each layer;

FIG. 2 illustrates a method of transmitting a signal by a transmitter ina beamforming system;

FIG. 3 illustrates a method of receiving a signal by a receiver in thebeamforming system;

FIG. 4 illustrates a phenomenon in which the different numbers ofsamples are acquired according to different beams at a sampling time;

FIG. 5 illustrates a beam state report process according to anembodiment of the present invention;

FIG. 6 is a flowchart illustrating a beam state information reportmethod according to an embodiment of the present invention;

FIG. 7 illustrates a sample selection method according to an embodimentof the present invention;

FIG. 8 illustrates a method of determining a cell priority according toan embodiment of the present invention;

FIG. 9 illustrates prioritized beam pairs per neighbor cell and cellpriorities according an embodiment of the present invention;

FIG. 10 illustrates a method of determining a cell priority based on anaverage of beam pairs larger than or equal to a threshold;

FIG. 11 illustrates a beam state measurement report procedure accordingto an embodiment of the present invention;

FIG. 12 is a block diagram illustrating a UE according to an embodimentof the present invention; and

FIG. 13 is a block diagram illustrating an eNB according to anembodiment of the present invention.

MODE FOR THE INVENTION

Hereinafter, various embodiments will be described with reference to theaccompanying drawings. It should be noted that the same elements will bedesignated by the same reference numerals although they are shown indifferent drawings. Further, a detailed description of a known functionand configuration which may make the subject matter of the presentinvention unclear will be omitted. Hereinafter, it should be noted thatonly the descriptions will be provided that may help understanding theoperations provided in association with the various embodiments of thepresent invention, and other descriptions will be omitted to avoidmaking the subject matter of the present invention rather unclear.

In embodiments of the present invention, measurement may be used as thesame meaning as that of beam measurement, beam state measurement, orbeaming channel state measurement. The beam state measurement mayinclude a channel state between a transmission beam of an eNB and areception beam of a UE or a state of a received signal intensity. Ameasurement report may be used as the same meaning as that of a beammeasurement report, a beam state measurement report, or a beam channelstate measurement report. A serving cell and a serving eNB may be usedas the same meaning. A neighbor cell and a neighbor eNB may be used asthe same meaning.

FIG. 2 illustrates a method of transmitting a signal by a transmitter ina beamforming system. Referring to FIG. 2, according to an embodiment ofthe beamforming system, the transmitter transmits a narrow beam in onedirection in one time slot, and then rotates and transmits a beam in anext neighbor direction in a next time slot. Neighbor directions may beseparated by a beam width. The beam transmitter may transmit controlinformation and reference signals in each beam. For example, a generalsynchronization and broadcast channel (SCH/BCH) is transmitted everyfour subframes among five subframes. In each subframe, the SCH/BCHshould be transmitted in each control beam direction. In a fifthsubframe, a reference signal for supporting measurement is transmittedin each beam direction. The reference signal may be similar to aCell-specific Reference Signal (CRS) of LTE.

FIG. 3 illustrates a method of receiving a signal by a receiver in thebeamforming system. Referring to FIG. 3, beamforming may be used toobtain a reception antenna gain by the receiver. In general, the numberof RF chains of the receiver is limited in consideration of expense andcomplexity. For example, when the receiver has only one RF chain, thereceiver adjusts an antenna in one direction at a time.

According to an embodiment of the present invention, the receiver mayinclude at least two reception chains (RX chains). It is assumed thatthe number of RX chains is two in FIG. 3. A first RX chain may be usedfor receiving data from a serving cell. The first RX chain may use abeam having a best reception rate among a plurality of reception beamsas a serving beam. The first RX chain may be selected based on ameasurement result of each TX beam and RX beam. A second RX chain may beused for measuring a beam state of a beam pair corresponding to thetransmission beam. The beam state measurement of the beam pair mayinclude not only measurement of the serving cell but also measurement ofthe neighbor cell.

The receiver is required to acquire reception energy in all directions.For example, when a beam width of the receiver is 90 degrees, four slotsare needed to acquire reception energy in all directions. Inconsideration of the beamforming system, acquiring one sample withrespect to one pair of TX beam and RX beam takes time, which correspondsto a product of a time required for transmitting a beam in eachdirection by a transmitter and a time required for acquiring receptionenergy in all directions.

For example, a simple system, in which the transmitter transmits a beamincluding a Reference Signal (RS) used by the receiver for measurementin each slot (in one beam direction in one slot), is considered. Thenumber of slots required for acquiring one sample with respect to eachpair of TX beam and RX beam is Ntx*Nrx. Ntx denotes the number of TXbeam directions and Nrx denotes the number RX beam directions. Forexample, when a TX beam width is 10 degrees, Ntx=36 to cover allomnidirectional spaces. When the RX beam width is 30 degrees, Nrx=12. Insuch a condition, in order to acquire one measurement sample withrespect to each beam pair, 36*12=432 slots are required.

Since a millimeter wave is more susceptible to penetration/absorption,millimeter wave links are much more fragile compared to sub 3 GHz links.For example, when the millimeter wave penetrates a human body, the humanbody causes a loss of 20-35 dB. Similarly, materials such as concreteand leaves may cause a significant loss. In such a system, a good linkrecognized by the receiver based on signal power received from thecorresponding link may be more quickly lost (compared to a general timescale of a measurement task). That is, although a beam having the goodreceiving sensibility is determined, the receiving sensibility mayrapidly deteriorate due to a sudden loss. In order to solve the aboveproblems, when one link is lost in the system configuration, a linkhaving the good receiving sensibility between the network and the UE maybe managed in advance to allow communication between other links toremain.

Continuous measurement for all beam pairs is required to evaluatedurability of the link and identify the best link (TX and RX beam pair).However, when all pairs are measured only for a short time, it takes aconsiderably long time to acquire the desired number of samples in lightof the high power of Ntx and Nrx used for the measurement. Further, whenthe beam states of all beam pairs are continuously measured, thefollowing problems may occur.

—Problem of a Different Number of Measurement Samples for Each BeamPair.

Based on the number of available RFs, one RF continuously focuses on abest serving beam pair. Other RFs should measure other beam pairscrossing over cells. In general, the number of RFs is highly likely tobe smaller than the number of beam pairs to be measured. Accordingly,more samples can be acquired with respect to the best serving beam pairrather than other beam pairs. That is, although many samples can beacquired with respect to the beam pair (serving beam pair) for RX 1,relatively few samples can be acquired with respect to beam pairs for RX2 compared to the serving beam pair in FIG. 3.

—Problem of Different Measurement Sample Collection Periods of BeamPairs.

A time for collecting measurement samples for all beam pairs may be muchlonger than a general channel coherence time. If a system usingmillimeter communication considers deep and frequent shade (linkvulnerability), the existing order samples cannot accurately reflectcurrent channel conditions. That is, in L1, a time for calculating ameasurement value average may be several times longer than the channelcoherence time depending on Ntx and Nrx. This results in a problem of amethod of standardizing samples within a sampling period.

This will be described with reference to FIG. 4. FIG. 4 illustrates thedifferent numbers of samples according to different beams during thesame sampling time. Referring to FIG. 4, more samples can be acquired inthe sampling average calculation time (L1) with respect to RX beam 1compared to RX beam 2, RX beam 3, and RX beam 4. In FIG. 4, RX beam 1may acquire three times more samples than beams included in RX chain 2(RX beam 2, RX beam 3, and RX beam 4). Accordingly, it is required todefine a proper standard mechanism to prevent inaccuracy of beamselection due to imbalance of the number of samples in the beamselection.

Further, the following problems need to be solved in the beamformingsystem. First, a method of determining a cell priority based on beampairs in the beamforming system is required. The number of beam pairs isa new parameter, which can be used to determine a priority of a celllist measured for cell selection/addition. In the millimeter wavesystem, when one link is blocked due to link vulnerability, an ongoingservice may be stopped. In order to solve the above problem, if a linkhas a problem, the UE is required to maintain a plurality of links ormanage a candidate group of beam pairs in order to easily use anotherlink.

Further, a method of defining a reporting event in the beamformingsystem is required. Performing the measurement report all the time whenthe measurement report information is collected is a pressure on the UEand is not efficient in power management. Accordingly, it is required todefine a condition for triggering the collected measurement report.

<Embodiment for Solving the Problem of the Number of Samples Accordingto Each Beam>

An embodiment of the present invention uses the following method tosolve the problem that the numbers of measurement samples with respectto beam pairs of the cell within the L1 average calculation period(also, referred to as a measurement period) are different. An embodimentof the present invention defines a measurement framework similar to thatof a legacy 4G system as a time period for filtering L1 and L3 inducedfrom the number of RX and TX beams in the system. For example, it isassumed that the number of TX beams Ntx is 27 and the number Ntx of RXbeams is 9 in FIG. 5. The sampling is performed for one beam pair every27 ms, and a measurement average may be calculated by 5 samples for onebeam pair. In this case, L1 and L3 average calculation periods includingfive samples with respect to one beam pair are set to 135 ms (inconsideration of the frame structure as illustrated in FIG. 2). In L3, apreset threshold and a final filtered value may be compared. Based on aresult of the comparison with the threshold, an event such as themeasurement report may be selected.

FIG. 6 illustrates a method of reporting beam state informationaccording to an embodiment of the present invention. Referring to FIG.6, in step S610, the UE may collect beam state information on each beampair of the serving cell and the neighboring cell. Beam stateinformation on a beam pair of each TX beam and each RX beam of theserving cell may be collected by the first reception chain. Beam stateinformation on a beam pair of each TX beam and each RX beam of thesecond reception serving cell may be collected.

In step S620, in order to solve the other aforementioned problem thatthe numbers of samples are different, the UE may apply weights to thecollected samples or select a sampling interval in which the same numberof samples are applied. The weight and sampling interval selection willbe described below in more detail.

In step S630, the UE may calculate a beam state average of the samplesto which the weights are applied or the samples included in the selectedsampling interval.

In step S640, the UE may report the beam state based on the beam stateaverage calculation or an evaluation result.

Hereinafter, the method of solving the number of samples of step S620will be described in more detail. According to an embodiment of thepresent invention, in order to standardize samples with respect to allbeam pairs, higher weights may be applied to recent samples based on thesampling time. This may be defined as “Recent Preferred WeightedAveraging (RPWA). A channel variation is higher and more frequent in themillimeter wave. Accordingly, it is required to depend less on values ofsamples, which have a relatively early sampling time, in the measurementaverage calculation in order to avoid selecting a non-optimized beam dueto old beam samples in the average calculation process. The weight forperforming RPWA may be predefined or preset by the network in abroadcast or unicast type.

In one method of the above embodiment, the weight of the sample may beinduced based on a weight decline factor “g” predetermined or preset bythe network. For example, a weight of a recent sample may be set to 1, aweight of a sample before the recent sample may be set to (1−g), and aweight of a sample before the sample set to (1−g) may be set to(1−g)*(1−g). In another example, the weight may be linearly reduced. Inanother example, the weight may be exponentially reduced. In anotherexample, a weight of a sample “x” may be explicitly given or predefinedby the network. A predefined value, for example, “0” may be used for asample before the sample “x”. In an example, the weight may be set to 1with respect to samples resulting in the linear average. In this case,the weight is not required to be explicitly defined. Instead, anindication of the linear average may be set by the network. Through sucha method, a highest weight may be assigned to a most recently measuredsample, and a lowest weight may be assigned to an oldest sample.

In another embodiment, averaging considers the same number of sampleswith respect to each beam pair. The number of samples may be set,predefined, or the same as the minimum number of samples selected withrespect to the beam pair in the average calculation period. FIG. 7illustrates a sample selection method according to an embodiment of thepresent invention. Selecting some of the collected samples may be equalto selecting a sampling interval in which samples of the collectedsamples are collected. Referring to FIG. 7, RX beam 1 has three timesmore samples than other beams during the average calculation period.When the number of available samples with respect to a particular beamis larger than the number of samples of other beams set for the averagecalculation, the average may be calculated using the same number ofsamples as that of the samples of the other beams. Meanwhile, when thenumber of available samples is too large and thus it is required toselect samples of other beams, recently acquired samples may be firstconsidered. The number of samples is counted from a time point when themeasurement average calculation period ends in a reverse order of thesampling, and the number of samples acquired at a time point when thenumber of samples becomes the same as the number of samples of anotherbeam may be used. Further, according to the present embodiment, thelinear average or the RPWA may be performed.

That is, an embodiment of the present invention proposes two methods tosolve the problem that the average is calculated using different numbersof measurement samples according to beams. A first method uses samplesacquired during a measurement average calculation period and a weight.In a second method, when the number of samples for a particular beam islarge, a sample candidate group for the measurement average calculation,which includes the same number of samples as that of another beam, isselected and the measurement average is calculated for the same samples.

The first method may have three options. A first option may performRecent Preferred Weighted Averaging (RPWA) for all samples collected foreach beam pair. A weight may be applied to the samples for each beam. Ahigh weight may be assigned to a most recently sampled beam sample and alow weight may be assigned to an old sample. Accordingly, the problemoccurring due to the different numbers of samples can be solved. Forexample, the weight may be applied to all samples of FIG. 7 inaccordance with a measurement time.

A second option may perform the RPWA only for a beam (for example, aserving beam) having the larger number of samples than other beams, andperform a linear average calculation for other beam pairs. For example,RX beam 1 corresponds to a beam which acquires the larger number ofsamples than other beams in FIG. 7. Accordingly, the RPWA may beperformed for RX beam 1. The linear average calculation may be performedfor the other beams.

A third option may perform the RPWA only for a beam having the largernumber of samples than other beams, perform the linear averagecalculation for other beam pairs, and assign a higher weight to recentlymeasured beams. In FIG. 7, the RPWA may be performed only for beam pairscorresponding to RX beam 1, and the linear average may be applied tobeam pairs corresponding to other beams (RX beam 2, RX beam 3, and RXbeam 4). The weight may be applied to the other beam pairs afterapplying the linear average. In the application of weights, a lowerweight than that of RX beam 4 may be applied to the average of beampairs corresponding to the RX beam 3. Accordingly, scaling down may beperformed. The average of beam pairs corresponding to RX beam 2 may bescaled down from RX beam 3.

A second method may apply the same number of samples to all beam pairsduring the average calculation period. With respect to each beam pair,recently selected “x” samples may be considered for the averagecalculation. For example, RX beam 1 possesses more samples and the otherbeams (RX beam 2, RX beam 3, and RX beam 4) acquire fewer samples inFIG. 7. When samples for the measurement average with respect to RX beam1 are selected to perform the average calculation with respect to thesame samples, the same number of samples as that of another beam may beselected as samples for the measurement average calculation. When thenumbers of samples of other beams are different, samples for themeasurement calculation may be selected from each beam such that thenumbers of samples of the beams become the same. After the same numberof samples is selected from each beam, the RPWA may be performed. Ahigher weight may be assigned to a recently measured beam. Further, thelinear average calculation may be performed.

At this time, the weight may be predefined, or may be configured by thenetwork in a broadcast or unicast type. Meanwhile, the number ofsamples, which should be considered in the average calculation process,may be predefined, or may be configured by the network in a broadcast orunicast type.

Alternatively, the number of samples, which should be considered in theweight and average calculation process, may be determined by the UEwithout any aid from the network. In this case, the number of samplesmay be determined based on present and past channel conditions observedby the UE. For example, the channel conditions may depend on movement ofthe UE.

<Embodiment of Determining Cell Priority Based on Beam Pair>

According to another embodiment of the present invention, a cellpriority may be determined after the average of measurement samples ofbeam pairs is calculated. Beam pairs having the calculated averagemeasurement value smaller than a threshold may be excluded from thecalculation considering a priority. The threshold may be predefined orpreconfigured. Since the number of beam pairs is large in a narrow beamwidth millimeter wave system, not all measurement values of beam pairsneed to be reported. Accordingly, after the measurement valuecalculation, when a particular reference is met, the measurement reportmay be performed. For example, after a priority is determined based onthe measurement value, the measurement report may be performed only forbeam pairs having a measurement value, which meets a threshold.

An embodiment of the present invention may provide a method ofdetermining a cell priority based on a beam pair. The cell priority mayrefer to a priority for selecting a cell, which provides a service tothe UE. A neighbor cell may also have the priority. According to anembodiment of the present invention, the priority of the beam pair maybe determined based on measurement samples. Further, the priority ofeach cell is determined based on the number of beam pairs larger than orequal to a threshold. Alternatively, a higher priority may be assignedto a cell having a larger average measurement value of the beam pair.Both the beam pair larger than or equal to the threshold and themeasurement average value of the cell may be considered.

Since a link variation is large in millimeter wave channel conditions,determining the priority of the beam pair within the cell may be useful.That is, when there is the link variation in the serving beam, anotherbeam should be selected. Such a situation frequently occurs in themillimeter wave system, so that selecting a cell having the large numberof good beams is useful for operations of the UE and the eNB. Further,when a cell is re-selected, selecting a high priority cell based on thepriority is advantageous.

FIG. 8 illustrates a method of determining a cell priority according toan embodiment of the present invention. Referring to FIG. 8, in stepS810, the UE may collect beam state information on each cell. In stepS820, the UE may calculate a beam state average of each cell based onthe collected beam state information. Since the collection of the beamstate information and the calculation of the beam state average of eachcell have been described above, detailed descriptions thereof will beomitted. Meanwhile, in considering the cell priority, when only thenumber of beams having a beam state larger than or equal to a thresholdis considered, step S820 may be omitted.

In step S830, the UE may select priorities of all cells from which beammeasurement information has been collected. The UE may select thepriority by using beam state measurement information. A detailed methodof selecting the priority will be described below.

In step S840, the UE may report a result of the priority selection tothe eNB. The eNB having received the result of the priority selectionmay use the result of the priority selection in replacing a serving cellfor the UE or selecting a new serving cell.

A method of determining the cell priority based on the beam state, whichcorresponds to a detailed operation of step S830, will be described inmore detail. In a first method, a higher priority is assigned to a cellhaving the larger number of beam pairs in a good state. In order todistinguish the beams in the good state, a threshold may be used. Withrespect to each beam, the channel state measurement value is comparedwith the threshold. Based on a result of the comparison, beam pairslarger than or equal to the threshold may be counted. The cell prioritymay be determined according to the number of beam pairs larger than orequal to the threshold based on a result of the count. The priority ofeach beam within the cell may be also determined.

FIG. 9 illustrates prioritized beam pairs per neighbor cell and cellpriorities according an embodiment of the present invention. Referringto FIG. 9, the eNB or the UE may manage a neighbor cell priority beampair list 910 and a cell priority list 930. First, the neighbor cellpriority beam pair list 910 may be a list of a priority of each beampair per cell. A channel measurement result may be acquired from eachbeam pair of each cell, and the threshold may be preset. With respect toeach beam, the channel state measurement value is compared with thethreshold. With respect to each beam pair, a beam pair having a channelstate larger than or equal to the threshold may be managed in theneighbor cell priority beam pair list 910. Priorities of beam pairs ofother cells may be updated in the neighbor cell priority beam pair list910.

The cell priority list 930 may be updated based on a result of theupdate. In the neighbor cell priority beam pair list 910, cell 1 hasfour beam pairs larger than or equal to a threshold (N1=4), cell 2 hasthree beam pairs larger than or equal to the threshold (N2=2), cell 3has two beam pairs larger than or equal to the threshold (N3=2), andcell 4 has one beam pair larger than or equal to the threshold (N4=1).That is, N1>N2>N3>N4. The cell priority list 930 may be updated based onthe number of beam pairs. Cell 1, which has the largest number of beampairs in the range larger than or equal to the threshold, has thehighest priority in the neighbor cell list. When the current servingcell has a link problem, cell 1, which has the largest number of beampairs having a good channel state, may be selected the serving cellbased on the priority.

Additionally, the cell priority may be determined based on priorities ofbeam pairs of TX beams for a particular RX beam per cell without the useof measurement results of beam pairs for all RX beams. In this case, theUE has the advantage of selecting a cell having the large number ofbeams in the best state with respect to the current RX beam whilemaintaining the currently used RX beam. Further, since the UE is notrequired to measure beams other than the current serving RX beam,complexity and power consumption can be reduced.

Meanwhile, the first method is based on only the number of beam pairshaving the good state in the cell, and thus cannot guarantee an entirecell measurement average, which is better than those of other cells.Accordingly, the second method suggests using the measurement averagefor all beam pairs of each cell, rather than using the number of beampairs larger than or equal to the threshold when determining the cellpriority.

According to an embodiment of the second method, an average of beampairs within each cell may be calculated, and the cell priority may bedetermined based on the calculated average. Rather than all beam pairswithin each cell, only the beam pairs within the cell, which are largerthan or equal to a threshold may be used to calculate the average, andthen priorities of cells may be determined based on the average of thebeam pairs.

FIG. 10 illustrates a method of determining a cell priority based on anaverage of beam pairs larger than or equal to a threshold. Referring toFIG. 10, the neighbor cell priority beam pair list is the same as thatdescribed in FIG. 9. For example, cell 1 has four beam pairs, which havean average M1 and are larger than or equal to the threshold, and cell 2has two beam pairs, which have an average M2 and are larger than orequal to the threshold. When M2>M1, cell 2 has a higher priority thancell 1. When beam pair 1 of cell 3 has an average sample value s1 andbeam pair 2 of cell 3 has an average sample value s2, an averagemeasurement value of cell 3 is (s1+s2)/2. In FIG. 8, it is assumed thatM4>M3>M2>M1. Accordingly, cell 4, which has the highest beam pairchannel state average, has the highest priority, and cell 1, which hasthe largest number of beam pairs larger than or equal to the threshold,has the lowest beam pair channel state average and thus has the lowestpriority.

Meanwhile, when the cell priority is determined based on the measurementaverage, the average may be calculated using the preset number of beampairs. For example, when the number of beam pairs is N and only threebeam pairs are considered for the average calculation process, only thepreset number of beams among the N beam pairs may be used to acquire theaverage measurement value per cell. At this time, a beam pair, which hasa high measurement value, among a plurality of beam pairs used for theaverage value may be first selected and used.

A third method may consider both the number of beam pairs larger than orequal to the threshold and the measurement average. Cells having thenumber of beam pairs, which is larger than a preset or predefined numberof beam pairs larger than or equal to the threshold, may be determinedas a first set. Cells having the number of beam pairs, which is smallerthan or equal to the preset number of beam pairs larger than or equal tothe threshold, may be determined as a second set. The cells determinedas the first set may be prioritized based on the number of beam pairs.The cells determined as the second set may be prioritized based on theaverage of beam pairs within the cell. The cells included in the firstset may have a higher priority than the cells included in the secondset. For example, it is assumed that cell 1 has five beam pairs largerthan or equal to the threshold, cell 2 has three beam pairs larger thanor equal to the threshold, cell 3 has two beam pairs larger than orequal to the threshold, and cell 4 has one beam pair larger than orequal to the threshold. For example, when it is assumed that the numberof beam pairs set to determine whether the cell is included in the firstset is 3, cell 1 and cell 2 are included in the first set, and cell 3and cell 4 are included in the second set. In this case, although themeasurement averages of beam pairs within cell 3 and cell 4 are largerthan the measurement averages of cell 1 and cell 2, cell 1 and cell 2included in the first set have a higher priority than cell 3 and cell 4included in the second set.

In a fourth method, according to an embodiment of the present invention,the remaining beam pairs may be prioritized within the correspondingcell later. Thereafter, the priority of each cell is determined based onthe number of beam pairs larger than or equal to the threshold.Subsequently, the cells are re-arranged, and cells having a differencein an average of received signal intensities of beam pairs larger thanor equal to the threshold and a difference in the number of beam pairssmaller than the threshold are prioritized. Such a procedure is repeateduntil priorities of all lists are determined. This has an advantage in asituation where the cell has a smaller number of beam pairs but has ahigher average rather than a situation where the cell has a largernumber of beam pairs but has a lower average.

In a fifth method, according to another embodiment of the presentinvention, the priorities of the cells are determined based on thenumber of beam pairs larger than or equal to the threshold ordynamically determined based on the average number of beam pairs withinthe cell. The UE may select a reference for the determination of thepriorities according to channel conditions, mobility, recent histories,or a combination of one or more thereof. For example, with respect tothe UE, which moves quickly, the channel conditions change more quickly,so that it is more important for the UE, which moves quickly, to haveone or more good beams from the serving cell. Accordingly, the UE, whichmoves quickly, may select the reference based on the number of beampairs larger than or equal to the threshold.

According to an embodiment, the threshold appropriate for the referencemay be configured by the network to allow the UE to properly select thereference. For example, the network may use the reference of the averageof beam pairs to determine the priorities when the UE moves at a lowspeed, and may use the reference of the number of beam pairs larger thanor equal to the threshold when the UE moves at a high speed.Alternatively, according to another embodiment, when the UE determinesthat a beam variation rate is high, the UE may use the reference of thenumber of beam pairs larger than or equal to the threshold. When the UEdetermines that the beam variation rate is low, the UE may use thereference of the beam pair average to determine the priorities.

As described above, in order to determine priorities of cells based onmeasurement results of beam pairs, the number of beam pairs larger thanor equal to the threshold and the average of beam pairs within the cellmay be used. Further, both the number of beam pairs and the average maybe considered together. Additionally, it may be determined which onebetween the number of beam pairs and the average is preferentiallyselected, based on channel conditions, mobility, or recent histories ofthe UE. Such various thresholds may be predefined or preset by thenetwork.

<Embodiment for Defining Reporting Event in Beamforming System>

According to an embodiment of the present invention, a new reportingevent is defined in the beamforming system. In a first type, an eventfor triggering a measurement report to a neighbor cell when a state ofthe serving cell is not good may be defined. According to an embodimentof the present invention, with respect to the serving cell or theneighbor cell, the measurement report to the neighbor cell is nottriggered until a particular condition related to beams of each cell ismet. This is to efficiently manage power of the UE by not performingswitching on a second RX chain (RX chain for the neighbor cell) when theserving cell or the neighbor cell does not meet the particular conditionin the beamforming system using a double RX chain.

In the first type, when the number of beams having the good state in theserving cell is smaller than a preset number or when the measurementaverage of the serving cell is smaller than a preset threshold, themeasurement report may be triggered.

In a second type, an event for triggering the measurement report whenthe state of the neighbor cell is good may be defined. In the secondtype, when the number of beams having the good state in the neighborcell is larger than or equal to a preset number or when the measurementaverage of the neighbor cell is larger than or equal to a presetthreshold, the measurement report may be triggered.

In a third type, an event for triggering the measurement report when thestate of the neighbor cell is relatively better than the state of theserving cell may be defined. The third type uses a relative relationshipbetween the neighbor cell and the serving cell. When the number of beamshaving the good state in the neighbor cell is larger than the number ofbeams having the good state in the serving cell or when the measurementaverage of the neighbor cell is larger than or equal to the measurementaverage of the serving cell, the measurement report t may be triggered.

An embodiment of the present invention will be described in more detailwith reference to FIG. 10. FIG. 10 illustrates a beam state measurementreport procedure according to an embodiment of the present invention.Referring to FIG. 10, the beamforming system may include a UE 1110, aserving eNB 1130, and at least one neighbor eNB 1150. A serving cell anda serving eNB may be used as the same meaning. The neighbor eNB may beused as the same meaning as that of the neighbor cell.

In step S1110, the serving eNB 1130 may transmit measurement reportconfiguration information to the UE 1110. The measurement reportconfiguration information may include first type, second type, and thirdtype measurement report trigger condition information. The measurementreport trigger condition may include a first condition, a secondcondition, a third condition, and a fourth condition. The firstcondition may be a condition of triggering a measurement report when thenumber of beam pairs having the beam state measurement value of theserving cell 1130, which is larger than or equal to a first threshold,is smaller than a preset number. The second condition may be a conditionof triggering a measurement report of the neighbor cell 1150 when thebeam state measurement average of the serving cell 1130 is smaller thana second threshold. The third condition may be a condition of triggeringa measurement report of the neighbor cell when the number of beam pairshaving the beam state measurement value of the neighbor cell 1150, whichis larger than or equal to a third threshold, is larger than or equal toa preset number. The fourth condition may be a condition of triggering ameasurement report of the neighbor cell 1150 when the beam statemeasurement average of the neighbor cell 1150 is larger than or equal toa fourth threshold. The first threshold and the third threshold may bethe same. The second threshold and the fourth threshold may be the same.

In step S1120, the UE 1110 may measure the beam state of the beam pairof the neighbor cell 1150. The UE 1110 may measure beam state of all RXbeams which can be received and all TX beams of the neighbor cell. Themeasurement for the neighbor cell 1150 may be periodically performed, ormay be aperiodically performed through reception of an instruction fromthe serving eNB 1130. The beam measurement for the serving cell 1130 maybe also performed. Before the measurement report trigger condition isreceived, the measurement for the neighbor cell 1150 may be performed.

In step S1130, the UE 1110 may determine whether the serving cell 1130or the neighbor cell 1150 meets the measurement report trigger conditionbased on a result of the measurement. When the number of beam pairs ofthe serving cell 1130, which meet the first threshold, is smaller than apreset number, it may be determined that the trigger condition is met.When the beam state measurement average of the serving cell 1130 issmaller than the second threshold, it may be determined that the triggercondition is met. When the number of beam pairs of the neighbor cell1150, which meet the third threshold, is larger than or equal a presetnumber, it may be determined that the trigger condition is met. When thebeam state measurement average of the neighbor cell 1150 is larger thanor equal to the fourth threshold, it may be determined that the triggercondition is met. Further, when the number of beams having a good state(beam pairs having the beam state measurement value larger than or equalto the third threshold) of the neighbor cell 1150 is larger than thenumber of beams having a good state (beam pairs having the beam statemeasurement value larger than or equal to the first threshold) of theserving cell 1130, or when the measurement average of the neighbor cell1150 is larger than or equal to the measurement average of the servingcell 1130, it may be determined that the trigger condition is met.

When it is determined that the measurement report trigger condition ismet in the previous step, the UE 1110 may perform the measurement reportin step S1140. The UE 1110 may perform the measurement report of theneighbor cell 1150. The measurement report may be the beam statemeasurement report. When it is determined that the measurement reporttrigger condition is not met in the previous step, the UE 1110 does notperform the measurement report of the neighbor cell 1150. Themeasurement report may include recent measurement results of beam pairsof the neighbor cell 1150. The measurement result may indicate a notgood beam state of the serving cell 1130. Further, the measurementresult may indicate that the beam channel state of the current neighborcell 1150 is better than the beam channel state of the serving cell.Moreover, the measurement result may indicate that the neighbor cell1150 has the larger number of beam pairs having a good channel statethan the serving cell 1130. Furthermore, the measurement report mayindicate that the neighbor cell 1150 has a higher measurement stateaverage than the serving cell 1130.

The serving eNB 1130 may receive the measurement report from the UE. Theserving eNB 1130 may select a new serving eNB of the UE based on aresult of the measurement report. Further, the measurement report may beused to determine a serving beam in the new serving eNB.

FIG. 12 is a block diagram illustrating a UE according to an embodimentof the present invention. Referring to FIG. 12, a UE 1200 may include atransceiver 1210 and a controller 1230. The controller 1230 may includeat least one processor. The transceiver 1210 may perform communicationwith at least one network node. The controller 1230 may control ageneral operation of the UE.

The controller 1230 may make a control to measure beam state informationby using a first RX chain and a second RX chain, control the beam stateinformation on the first RX chain to correspond to the beam stateinformation on the second RX chain, calculate state information on eachbeam based on the beam state information on the first RX chain and thebeam state information on the second RX chain, and report stateinformation on at least one beam. At this time, the first receptionchain may be a chain for collecting a beam state of a serving receptionbeam, and the second reception chain may be a chain for collecting beamstate of other reception beams except for the serving reception beam.

The controller 1230 may make a control to measure beam state informationon beams of at least one serving cell and beams of at least one neighborcell, adjust beam state information on at least one measured beam fornormalizing the beam state information on the measured beam, calculatestate information on each beam based on the adjusted beam stateinformation and report state information on one or more beams.

The controller 1230 may make a control to adjust the beam stateinformation on the second reception chain by assigning weights to thesamples of the beam state information collected through a reception beamof the terminal. The recently collected samples of a beam are assignedhigher weight value as compared to other collected samples of the samebeam that are considered for normalization. The weight can be configuredby the network to the UE in broadcast or unicast manner. The weight canbe pre-specified.

The controller 1230 may make a control to adjust the number of samplesof the beam state information collected through the first receptionchain to be equal to the number of samples of the beam state informationcollected through one reception beam of the second reception chain. Theconsidered beam samples of the serving reception beam are the recentmost samples corresponding to the said number of samples. The consideredbeam samples of the serving reception beam are the samples in time thatcorrespond to the considered samples of the reception beam with theexception of the serving reception beam. The controller 1230 may make acontrol to apply a weight to a sample of a recently collected receptionbeam among the samples of the beam state information collected througheach reception beam of the second reception chain.

The controller 1230 may make a control to measure beam state informationon a neighboring cell, and determine a priority of the neighboring cellbased on the beam state information. At this time, the priority may bedetermined based on a parameter for the number of beam pairscorresponding to a cell having channel state information larger than orequal to a preset threshold or a parameter for beam state averageinformation on each neighboring cell. The priority is determined basedon the average sample measurement value across all beams correspondingto a cell. The priority is determined based on number of beam pairscorresponding to a cell and on the average sample measurement valueacross all beams corresponding to a cell.

The controller 1230 may make a control to select the parameter used fordetermining the priority from the parameters based on a channelcondition, mobility of the UE, and recent history information on the UE.

The controller 1230 may make a control to report the beam stateinformation on the neighboring cell based on information on the numberof beam pairs of the serving cell, which has beam state informationequal to or smaller than a preset first threshold, or information on thenumber of beam pairs of the neighbor cell, which has beam stateinformation larger than or equal to a preset second threshold. Thereporting the beam state information on the neighboring cells furthercorrespond to reporting only a preset number of beam state informationamong the list of prioritized beams

Although it has been described that the configuration of the UE 1200 isdivided into the transceiver 1210 and the controller 1230, this is onlyan embodiment and the configuration of the UE 1200 is not necessarilylimited thereto. Further, although the function and operation of the UE1200 have been described, the function and operation of the UE is notlimited to the description of FIG. 12 and the function and operationdescribed in FIGS. 1 to 11 according to the present invention may beperformed.

FIG. 13 is a block diagram illustrating an eNB according to anembodiment of the present invention. Referring to FIG. 13, an eNB 1300may include a transceiver 1310 and a controller 1330. The controller1330 may include at least one processor. The transceiver 1310 mayperform communication with at least one network node. The controller1330 may control a general operation of the eNB. According to anembodiment of the present invention, the eNB 1300 may transmitconfiguration information to allow the UE to perform the operationsillustrated in FIGS. 1 to 12. The configuration information may be beamstate information report configuration information.

The controller 1330 may make a control to transmit beam stateinformation report configuration information to at least one UE and toreceive beam state information from the UE based on the beam stateinformation report configuration information. At this time, the beamstate information may be determined based on information generated byadjusting the beam state information measured using the first RX chainand the second RX chain to correspond to the beam state information onthe second RX chain by the UE. Further, the first RX chain may be achain for collecting a beam state of a serving reception beam, and thesecond reception chain may be a chain for collecting beam state of otherreception beams except for the serving reception beam among the RX beamsof the UE.

The controller 1330 may make a control to transmit beam stateinformation report configuration information to a terminal and receivebeam state information from the terminal based on the beam stateinformation report configuration information. The beam state informationis determined based on information, which is generated by adjusting thebeam state information measured by the terminal for normalizing.

The beam state report configuration information may include information,which is configured to determine the beam state information by assigningweights to recently collected samples among samples of the beam stateinformation collected through the first reception chain or determine thebeam state information by adjusting the number of samples of the beamstate information collected through the first reception chain to beequal to the number of samples of the beam state information collectedthrough one reception beam of the second reception chain.

The controller 1330 may make a control to receive priority informationon neighbor cells from the UE. At this time, the beam state informationreport configuration information may include information, whichdetermines the priorities based on a parameter for the number of beampairs having channel state information larger than or equal to a presetthreshold of the UE or a parameter for beam state average information oneach neighboring cell. The beam state information report configurationinformation may include information, which is configured to report thebeam state information on the neighboring cell based on information onthe number of beam pairs of the serving cell, which has beam stateinformation equal to or smaller than a preset first threshold, orinformation on the number of beam pairs of the neighbor cell, which hasbeam state information larger than or equal to a preset secondthreshold.

Although it has been described that the configuration of the eNB 1300 isdivided into the transceiver 1310 and the controller 1330, this is onlyan embodiment and the configuration of the eNB 1300 is not necessarilylimited thereto. Further, although the function and operation of the eNB1300 have been described, the function and operation of the eNB are notlimited to the description of FIG. 13 and the functions and operationsdescribed in FIGS. 1 to 12 according to the present invention may beperformed.

The embodiments disclosed in the present specifications and drawingswere provided merely to readily describe and to help a thoroughunderstanding of the present invention but not intended to limit thescope of the present invention. Therefore, it should be construed that,in addition to the embodiments disclosed herein, all modifications andchanges or modified and changed forms derived from the technical idea ofthe present disclosure fall within the scope of the present disclosure.

1. A method by a terminal, the method comprising: receiving measurementreport configuration information including first information associatedwith a number of measurement results per beam from a base station;measuring a plurality of beams transmitted from a base station based onthe measurement report configuration information; deriving a measurementresult based on measurement values of the plurality of beams; andtransmitting the measurement result to the base station, wherein anumber of the measurement values is determined based on the firstinformation.
 2. The method of claim 1, wherein the measurement result isderived by averaging the measured values of the plurality of beams abovea threshold value indicated based on second information.
 3. The methodof claim 1, wherein the number of the measurement values is equal to orless than the number of the measurement results per beam.
 4. The methodof claim 2, wherein the second information is received from the basestation, and wherein a report of the measurement result is triggeredbased on a threshold value for a measure report.
 5. The method of claim1, wherein the first information indicates a maximum number ofmeasurement values to be averaged per beam.
 6. A terminal comprising: atransceiver; and at least one processor configured to: receivemeasurement report configuration information including first informationassociated with a number of measurement results per beam from a basestation, measure a plurality of beams transmitted from a base stationbased on the measurement report configuration information, derive ameasurement result based on measurement values of the plurality ofbeams, and transmit the measurement result to the base station, whereina number of the measurement values is determined based on the firstinformation.
 7. The terminal of claim 6, wherein the measurement resultis derived by averaging the measured values of the plurality of beamsabove a threshold value indicated based on second information.
 8. Theterminal of claim 6, wherein the number of the measurement values isequal to or less than the number of the measurement results per beam. 9.The terminal of claim 7, wherein the second information is received fromthe base station, and wherein a report of the measurement result istriggered based on a threshold value for a measure report.
 10. Theterminal of claim 6, wherein the first information indicates a maximumnumber of measurement values to be averaged per beam.
 11. A method by abase station, the method comprising: transmitting measurement reportconfiguration information including first information associated with anumber of measurement results per beam to a terminal; transmittingsignals based on a plurality of beams to the terminal; and receiving ameasurement result from the terminal, wherein the measurement result isderived based on measurement values of the plurality of beams, andwherein a number of the measurement values is determined based on thefirst information.
 12. The method of claim 11, wherein the measurementresult is derived by averaging the measured values of the plurality ofbeams above a threshold value indicated based on second information. 13.The method of claim 11, wherein the number of the measurement values isequal to or less than the number of the measurement results per beam.14. The method of claim 12, wherein the second information is receivedfrom the base station, and wherein a report of the measurement result istriggered based on a threshold value for a measure report.
 15. Themethod of claim 11, wherein the first information indicates a maximumnumber of measurement values to be averaged per beam.
 16. A base stationcomprising: a transceiver; and at least one processor configured to:transmit measurement report configuration information including firstinformation associated with a number of measurement results per beam toa terminal, transmit signals based on a plurality of beams to theterminal, and receive a measurement result from the terminal, whereinthe measurement result is derived based on measurement values of theplurality of beams, and wherein a number of the measurement values isdetermined based on the first information.
 17. The base station of claim16, wherein the measurement result is derived by averaging the measuredvalues of the plurality of beams above a threshold value indicated basedon second information.
 18. The base station of claim 16, wherein thenumber of the measurement values is equal to or less than the number ofthe measurement results per beam.
 19. The base station of claim 17,wherein the second information is received from the base station, andwherein a report of the measurement result is triggered based on athreshold value for a measure report.
 20. The base station of claim 16,wherein the first information indicates a maximum number of measurementvalues to be averaged per beam.